The invention relates generally to the field of electrosurgery, and more particularly to electrosurgical procedures which are performed within a body cavity which is filled or distended with a liquid. In one particular aspect, the invention relates to electrosurgical procedures for performing endometrial ablation and resection.
Electrosurgical procedures have become widely used to treat a variety of ailments including those associated with the uterus, such as uterine wall resection, endometrial ablation, endometrial resection, submucous myoma resection, intramural myoma resection, transmural myoma resection, and resection of the cervix and the cervical canal. Other electrosurgical procedures include kidney resection (laparoscopy), prostate resection (cystoscopy), ovary resection, removal of lung tissue and tumors (thoracoscopy), and the like. Of these electrosurgical procedures, those dealing with the treatment of the uterus are of particular interest.
Menorrhagia, or abnormal uterine bleeding, is a frequent clinical problem encountered by gynecologists. One common procedure for dealing with such abnormal bleeding is through the performance of a hysterectomy. In the United States, it is estimated that about 650,000 hysterectomies are performed each year. However, the performance of hysterectomies is becoming more and more undesirable, especially as new techniques and procedures have been developed to treat abnormal bleeding in a less intrusive manner. For example, a recent development is the use of hysteroscopic surgery employing laser or high frequency electrosurgical energy to destroy or remove the endometrium and a portion of the myometrium using direct visualization. Such procedures have been effective in significantly reducing menstrual blood flow and in decreasing secondary dysmenorrhea. For example, one exemplary device and method for performing both endometrial resection and ablation is described in U.S. Pat. No. 5,456,689, the disclosure of which is herein incorporated by reference. Other exemplary resection/ablation devices are described in copending U.S. application Ser. Nos. 08/322,680, filed Oct. 13, 1994, (attorney docket number 16944-00110); and 60/008,225, filed Nov. 8, 1995 (attorney docket no. 16944-001200), the complete disclosures of which are herein incorporated by reference.
Such electrosurgical resection/ablation devices are usually configured to employ monopolar current when used within an open body cavity, such as the uterus. With monopolar current, the cutting or ablation surface usually consists of an active electrode and a conductive pad return electrode which is applied to the patient's skin. Hence, the current flowing from the active electrode disperses into a low current field which terminates in the return electrode. The return electrode is large enough to reduce the current density to a level that is low enough to prevent the skin from becoming injured (burned) by the return current. Although small, there is some risk that the cutting current traveling from the inside wall of the uterus to the return pad could become concentrated in some delicate tissue, such as the bowel, which happens to be touching the outside of the uterus.
Another concern with the use of electrosurgical procedures within a body cavity such as the uterus is that the body cavity usually needs to be distended so that the desired tissue may be adequately visualized and so that enough room is provided to manipulate the surgical instrument. To distend the uterus, an electrically insulated fluid is generally employed. Common non-conductive distention fluids include Sorbitol, Glycine, Sorbitol-Mannitol or Mannitol. However, such fluids can in certain circumstances pose a danger to the patient. For example, if excessive quantities are absorbed into the patient's circulation, pulmonary edema may result. Further, since such fluids are electrolyte-free, they will, when absorbed in excess, produce plasma dilution of sodium, potassium and other electrolytes. This in turn may produce cardiac problems. Such a fluid may also cause water to transfer into brain cells, producing cerebral edema. Finally, Glycine is metabolized in the body and broken down into ammonia. Such a toxic substance can produce disturbances of consciousness, coma, or even death.
To avoid the risk of such complications, fluid loss (the difference between distention fluid used and fluid recovered from the procedure) is carefully monitored during the procedure and distention pressure is controlled to the minimum required for visualization. Such procedures are described in, for example, copending U.S. application Ser. No. 60/006,408, filed Nov. 9, 1995 (attorney docket no. 16944-000710), the disclosure of which is incorporated herein by reference.
The use of electrolyte solutions to distend the uterus have generally been dismissed for use with electrosurgery since the high frequency current is dispensed in all directions and thereby reduces the possibility of obtaining coagulation or cutting at the tissue/electrode interface. More specifically, when radio frequency current is used within an environment containing a non-conductive fluid, the current supplied to the active electrode passes directly into the tissue contacting the electrode, rather than through the non-conductive fluid. Hence, the power is dissipated within the body in a generally hemispherical pattern. Moreover, since current is delivered through only a portion of the active electrode, the current density at the active electrode is sufficient to resect or coagulate tissue. When the non-conductive fluid is replaced with a conductive fluid, the power supplied at the active electrode dissipates in a generally spherical pattern. This in turn reduces the current density at the active electrode so that effective resection or coagulation cannot occur.
Hence, for these and other reasons, it would be desirable to provide systems, methods and apparatus which would provide a safer environment when using electrosurgical procedures, particularly in combination with a distention fluid. Such systems, methods and apparatus should reduce or eliminate the risks associated with the use of nonconductive distention fluids. The systems, methods and apparatus should further prevent or reduce the possibility of unwanted current buildup within the body.